Known heads-up display (HUD) systems used in vehicles such as cars and airplanes provide a vehicle operator with computer-generated virtual graphics that augment the operator's visual sensory perception of real-world objects viewable to the operator during vehicle operation. The HUD systems may be configured to generate virtual graphics and project the virtual graphics as images or text through the windshield so that the operator can view the information while holding their heads up and without taking their attention away from the real-world objects viewable during vehicle operation. When the distance to the real object and the perceived distance to the virtual graphic generated by HUD do not match, it may cause discomfort to the driver and might result in additional delay because the human eye will take a certain amount of time to refocus and converge for a different distance each time the driver takes a look at a different object.
On HUD systems designed for airplanes in particular, most objects of interest may be farther than 100 meters away from the airplane so it may be assumed that an airplane HUD with a fixed focal distance locked at infinity would provide satisfactory results for the airplane pilot.
For objects located distances of 100 meters or more, the human eye focuses on the object as if it was located infinitely far away because the rays of light that are reflected from the object essentially arrive at the operator as parallel light rays. Accordingly, the computer generated virtual graphics of known HUD systems for airplanes may be displayed to the operator to appear at an image plane set at infinity to match the focal plane of other objects visible to the operator.
Road vehicles, e.g., automobiles, present a different environment for HUD systems since objects visible to the operator are often much closer than these objects appear to airplane pilots (e.g., less than 100 meters). A HUD image set to infinity or some other arbitrary distance in many scenarios may force the operator to refocus between the HUD-generated virtual graphic and the associated real world object, as a result of the discrepancy between focal distances (unlike most airborne airplanes). Known HUD systems designed for road vehicles may be set with a fixed focal plane of between 7.5 meters to 20 meters to be in the middle of a typical focal range. The HUD system focal plane may be set at a time of manufacture to approximate the typical distances to objects of interest outside a vehicle.
Since road vehicles may operate in vastly different road environments, e.g., crowded highways, suburban streets, or open country roads, the focal plane selected by the HUD manufacturer may not be optimized for a particular road environment. Overlaying computer generated virtual graphics on an object associated with a different focal plane may make the virtual graphics appear out of focus to the operator, or create confusion for the operator if it is not clear which object is associated with the virtual graphics.
A need remains for improvements in HUD systems.